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PSY 346 (30)
Lecture 22

PSY 346 Lecture 22: Diet and Exercise
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4 Pages
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Department
Psychology
Course Code
PSY 346
Professor
Johanna Jarcho

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Diet and Exercise Body Mass Index • BMI: (weight*703)/height • People who are overweight and extremely obese have generally always been that way, but obesity rates have risen Is Dieting the Answer to the Problem of Obesity? • Dieting: restricting caloric intake to lose weight • Should doctors recommend diets to treat obesity? • Clinical trials should help determine this o Phase 1: test safety (first in non-humans, then in humans) o Phase 2: test efficacy o Phase 3: compare efficacy of new treatment against existing gold standards Definitions of Diet Success Example: 200 pound women, 5’ 5”, BMI=33 Year Standard Pounds to lose Weight BMI 1940s Metropolitan 66 134 23 life; insurance tables 1950s Lose 40 pounds 40 160 27 1960s Lose 20 pounds 20 180 30 1970s Lose 10% of 20 180 30 starting weight 1995+ Lose 5% of 10 190 32 starting weight **And keep it off for a year since you started your diet **And keep it off for an extended period of time after the diet Long-Term Diet Studies • Studies with control groups (n=21) o Average weight change of dieters: lost 2 pounds o Average weight change of controls: gained 1 pound • Studies without control groups (n=13) o Initial weight loss: 39 pounds o Ultimate gain-back: 32 pounds o % who regain more than they lost: 31% to 64% o Systematic bias Bias 1: Self-Reported Weights • Independent evidence: people under-report their weight by about 8 pounds, and obese people tend to under-report by more than that • 61% of all follow-up weights in these studies were self-reported Bias 2: Participation in Additional Diets • Independent evidence: survey of dieters o 60% weighed more than starting weight at some point since diet o 40% weigh more than starting weight now • Rates of participation in other diets o 20% to 65% of participants Women’s Own Definitions of Diet Success • Almost 50% of them failed to reach the “Disappointing” rate • Many did not lose any weight at all Mechanisms of Diet Failure Biological Pathways Negative calorie balance Leptin and Insulin decrease Decrease metabolism Short term weight loss Ghrelin increase Increase food intake Catabolic inhibition Increased fat deposition Cholecystokinin sensitivity Anabolic stimulation Biopsychosocial Pathways Stress HPA Activation SNS Activation Weight Dieting Negative health behaviors Regain Increased food intake Psychological Pathways Violation/perceived violation of diet Overeating
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